[docs] [issue29920] Document cgitb.text and cgitb.html

Berker Peksag added the comment: Please don't close it yet. I agree with Serhiy's comments in msg293394, but I couldn't find time to address his comments yet (plus we still need to backport the documentation update to 3.5 and 3.6 branches) ---------- _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue29920> _______________________________________